In time-of-flight (TOF) depth imaging, a subject is irradiated by pulsed or otherwise modulated probe light. Some of the probe light reflects back from the subject to an imaging photodetector. The pixel elements of the photodetector are addressed in groups, in synchronicity with the modulated probe light. In this approach, the integration periods for the different groups of pixel elements may differ in phase or in total integration time, such that a pixel-resolved time of flight of the probe light from its origin at the probe emitter, out to the subject, and back to the photodetector, is discernible based on the relative amounts of light received in corresponding elements of the different groups. From the time of flight computed at a given pixel of the photodetector, the depth of the subject locus imaged by that pixel—i.e., the distance away from the depth camera—is computed.
In the approach summarized above, the signal-to-noise ratio for depth measurement may be eroded by indirect reflection of the probe light from one subject locus to another, and then to the photodetector. The prolonged time of flight of indirectly reflected probe light may falsely increase the measured depth of the second locus. For this reason, systematic measurement error may be observed with subjects prone to indirect reflection.